Adsorption of phenol onto garlic peel: optimization, kinetics, isotherm, and thermodynamic studies

In the present study, optimization of phenol adsorption onto garlic peel (GP) was conducted with process parameters such as initial pH, adsorbent dosage, agitation speed, and contact time. The percentage removal of phenol was optimized based on these process parameters. Response surface methodology was used for optimization as it has many advantages over classical optimization methods. A Box–Behnken experimental design was employed. The optimum conditions for maximum removal of phenol from an aqueous solution of 50 mg L−1 were found as follows: pH: 2, adsorbent dosage: 2.1g L−1, contact time: 7 h, and agitation speed: 135 rpm. At these optimized conditions, batch adsorption experiments were conducted to study the effects of initial concentration and temperature on phenol removal. Thermodynamic parameters such as ΔG∘,ΔH∘ and ΔS∘ were also evaluated. From the results, the sorption process was found to be spontaneous and exothermic. The equilibrium experimental data were analyzed with several isotherm models. The adsorption kinetics for phenol removal by GP follows the pseudo-second-order kinetic model. The results from the study demonstrated that more than 80% phenol removal is possible at the above-mentioned optimum conditions.